Digital Picture Exchange (DPX) files aren’t super well known to those outside the media and entertainment industry. But that doesn’t mean they’re not super important.
That’s because DPX files are the linchpin of the digital intermediate (DI) process. It’s a form of movie finishing that traditionally involved digitizing a motion picture originally captured on film. It now often alludes to color grading work before a film is finalized.
DPX files are a critical part of the post-production process for many productions. But what exactly are DPX files?
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What are DPX Files?
DPX Files are raster files, another term for two-dimensional images made of pixels. DPX files are mostly for digital intermediate and visual effects. Because each DPX file represents a single frame and can be ordered with other DPX files to form a sequence, a folder of DPX still frames can be likened to the “digital version of a roll of film.”
DPX files are lossless, uncompressed, and value image quality above all else. That means they’re usually very large. DPX is defined by a Society of Motion Picture and Television Engineers (SMPTE) standard.
Also known as the “Digital Moving Picture Exchange Bitmap,” DPX files typically include four sections:
- Generic image data: File and image information. Core fields in this section include image orientation, total image size in bytes, number of image elements, pixels per line, bit depth, encoding, and colorimetric specifications)
- Industry-specific information: Information that describes the source the image comes from (i.e. camera and film data), such as film manufacturing ID code, film type, frame position in the sequence, and sequence length
- User-defined data (optional): Customized information that defines any non-standard technical specs
- Image data: Bitmap pixel data
DPX file format: The basics
Because DPX files are of such high quality, they’re generally the file type of choice for high-end production workflows such as visual effects (VFX), shot manipulation, and archiving for future use.
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History of DPX Files
DPX wasby Kodak and is based on the relatively obscure Kodak Cineon file format (.CIN). It was subsequently further developed and is now maintained by SMPTE, with version 1 of SMPTE’s DPX format released in 1994 and version 2 in 2003.
What are DPX Files Used For?
Traditionally, DPX files are for transferring and storing images from film into a digital format without losing quality. Films scanned to DPX produce a lossless, numbered digital file corresponding to every frame.
DPX files are still popular in Hollywood’s post-film era because they’re great for VFX and color grading – specifically, because of the way DPX files store color data. DPX files store color density information but don’t “bake in” color information (as is done under the telecine process), making them easier to grade to match a production’s specific color palette.
Why are DPX Files So Heavy?
As mentioned up top, DPX files are lossless, uncompressed, and predicated around very high image quality. Combine these elements with the fact that one DPX file represents just one frame of footage, and the reasons behind the well-known heaviness of DPX files and folders becomes fairly obvious.
A film shot at 30 frames per second (fps) will create 30 DPX files for every second of footage.
Here’s a loose guide to the estimated sizes of 24 fps DPX files, based on resolution and bitrate:
|DPX (@ 23.976 fps)||Size Per Minute||Size Per Hour|
|1080p RGB 10bit||11.1GB||665 GB|
|1080p RGB 16 bit||16.6GB||1 TB|
|UHD RGB 10 bit||44.5GB||2.7 TB|
|UHD RGB 16 bit||66GB||4 TB|
|8K RGB 10 bit||177GB||10.6 TB|
|8K RGB 16 bit||266GB||16 TB|
You read that right – an hour-long video of 8K, 16-bit DPX files clocks in at around 16 TB.
Do I Need Special Hardware to Run DPX Files?
The gargantuan size of DPX files and sequences means you’re going to need some special hardware. DPX files require heavy-duty computing power, specifically on the storage side of things.
Hardware experts recommend storage with a read speed of at least twice that of the footage bitrate (between 400 MB/s and 2.2GB/s when working with 4K DPX files). Options for achieving such rates include setting up RAID configurations of multiple solid-state drives (SSDs) or using speedy Non-Volatile Memory Express (NVMe) drives.
CPU and GPU requirements for working with DPX files aren’t as drastic. Chips that play well with codecs like ProRes and DNx should be more than sufficient.
How to Send DPX Files?
And then there’s the whole question,
“How the heck am I going to transfer these DPX files to my partners and clients?”
It’s a good question because most large file transfer solutions can’t handle DPX-like file sizes. Try sending a few DPX files under WeTransfer Pro’s 20 GB file size limit, and then get back to us.
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